A worker vacuums contamination Thursday along the shore of Sand Creek where it meets the South Platte River north of downtown Denver. EPA officials said the muck leaking into the water is “a gasoline-like material” that contains cancer-causing benzene.

State health regulators on Thursday issued orders formalizing cleanup work already in progress to stanch the the flow of hazardous liquid seeping into Sand Creek and addressing newly identified contamination spreading underground from Suncor Energy’s refinery to an adjacent Metro Wastewater plant.

U.S. Environmental Protection Agency cleanup coordinators determined that the black goo oozing from the bank of Sand Creek north of downtown Denver is “a gasoline-like material” that contains cancer-causing benzene. Highly toxic, benzene has been linked to leukemia, and federal authorities have determined that even minute amounts are harmful.

EPA lab test results released Thursday evening indicate benzene concentrations ranging from 2,000 parts per billion, where the liquid enters Sand Creek, to 480 ppb, where the creek enters the South Platte River — well above the 5 ppb national drinking-water standard.

Battling snow, freezing temperatures and mud, workers contracted by Suncor and the EPA pushed ahead, digging 50 feet of a trench to be lined with gravel and plastic — to catch and contain the liquid as it seeps from the shoreline, preventing further contamination of the creek and South Platte River.

Workers inside “hot zone” boundaries rotated shifts against the cold, using heavy machinery to buttress absorbent booms strung across the creek as currents flowed faster and higher as a result of the snowfall.

Suncor is taking “all the action that we believe is necessary,” said John Gallagher, company vice president for refining.

But there’s no easy end in sight to the situation in this industrial zone — a situation that over the past year took a turn for the worse with new hydrocarbon and dissolved petroleum compounds moving in groundwater and surfacing as vapors in nearby Metro Wastewater buildings.

The state Hazardous Materials and Waste Management Division order requires Suncor to conduct daily inspections along Sand Creek; sample water along the creek; monitor air at the Metro Wastewater plant (for benzene, ethylbenzene, toluene, xylenes) and install ventilation systems if necessary; investigate groundwater contamination under the plant; install by Dec. 31 a system to intercept all liquids entering Sand Creek; and clean up any oil on the banks of Sand Creek and the South Platte by March.

Gallagher said Suncor officials were reviewing the order.

“I don’t anticipate there’s going to be anything in there that is a big surprise,” he said. “We have been working cooperatively with the EPA and will continue to do so. This is a formalization of that effort.”

Even before Suncor bought the refinery from Conoco in 2003, pollution now migrating to the wastewater plant — where one building is partly closed and workers have been forced to wear respirators — was documented. Oil refineries have existed at the Suncor property under various owners since the 1930s.

About 300 groundwater wells have been drilled around the property and at the wastewater plant to track contamination — 25 of them capable of recovering liquids.

Much of what regulators have been monitoring is described as “legacy contamination,” consisting of “mostly tarry asphaltic pockets of petroleum products underground that have not been moving,” said Warren Smith, a state health department spokesman.

Since the 1980s, state hazardous materials unit corrective action leader Walter Avramenko and others have been pushing for a cleanup, Smith said.

“Over the past year, there have been observed changes in the water quality in those monitoring wells on Suncor’s property. That suggests something new is happening that is not the legacy contamination,” Smith said. “Over the past year, we started noticing this.”

An Oct. 26 letter ordered Suncor to take corrective action.

On Sunday morning, a fisherman reported the latest spill into Sand Creek and the South Platte after wading into the muck. The state relied on the Tri-County Health Department to check out the report, and Tri-County could not find an oil sheen on the water.

The fisherman wrote a blog post that was read by a man in Boise, Idaho, who left a voice message at The Denver Post. Post queries Monday included a check with an EPA duty officer. That officer dispatched Kimbel, who smelled and then found the mess and launched an EPA response Monday afternoon.

Health officials still are trying to determine whether the newly discovered pollution migrating in groundwater is related to the ooze leaking into Sand Creek.

“The contamination is evidently more extensive and mobile than originally believed and conditions in the subsurface may be changing in response to seasonal influences,” Avramenko said in the order served Thursday, “all of which may have caused the contamination to express itself in the form of one or more seeps discharging into Sand Creek and vapors intruding into buildings overlying the plume.”

Suncor processes 93,000 barrels of crude oil per day to produce gasoline, diesel fuel and paving-grade asphalt. About 85 percent of the crude oil processed in Commerce City comes from Colorado and Wyoming, Gallagher said. Suncor also refines oil sand crude from Canada.

Bruce Finley covers environment issues, the land air and water struggles shaping Colorado and the West. Finley grew up in Colorado, graduated from Stanford, then earned masters degrees in international relations as a Fulbright scholar in Britain and in journalism at Northwestern. He is also a lawyer and previously handled international news with on-site reporting in 40 countries.